1. Field of the Invention
The present invention relates to oil field tools. More specifically, the invention relates to an apparatus for and a method of using a motor in a tubular member disposed in a wellbore.
2. Background of the Related Art
Historically, oil field wells are drilled as a vertical shaft to a subterranean producing zone forming a wellbore, the wellbore is lined with a steel tubular casing, and the casing is perforated to allow production fluid to flow into the casing and up to the surface of the well. In recent years, oil field technology has increasingly used sidetracking or directional drilling to further exploit the resources of productive regions. In sidetracking, an exit, such as a slot or window, is cut in a steel cased wellbore typically using a mill, where drilling is continued through the exit at angles to the vertical wellbore. In directional drilling, a wellbore is cut in strata at an angle to the vertical shaft typically using a drill bit. The mill and the drill bit are rotary cutting tools having cutting blades or surfaces typically disposed about the tool periphery and in some models on the tool end.
Generally, components including an anchor, a whipstock coupled to the anchor and a rotary cutting tool that progresses downward along the whipstock are used to cut the angled exit through the casing in the wellbore. The whipstock is an elongated cylindrical wedge-shaped member having an inclined concave deflection surface and guides the angle of the rotary cutting tool progressively outward to cut the exit. One or more of the components are attached to a tubing member, such as drill pipe or coiled tubing, that is used to lower the components into the wellbore. The anchor typically is a bridge plug, packer or another supporting or sealing member. The anchor is set in a downhole position and extends across the wellbore to form an abutting surface for placement of subsequent equipment. The anchor can be secured in the wellbore by mechanical or hydraulic actuation of a set of jaws directed outward toward the casing or wellbore. Hydraulic actuation generally requires a fluid source from the surface that pressurizes a cavity in the anchor to actuate the jaws.
Three “trips” have been used in past times to cut the exit in the casing, using an anchor, a whipstock and a cutting tool. A trip generally includes lowering a tubular member with a cutting tool or other component into the wellbore, performing the intended operation, and then retrieving the members to the surface. The first trip sets the anchor in the wellbore, the second trip sets the whipstock to the anchor and the third trip actuates the cutting tool to cut the exit along the whipstock. Such operations are time consuming and expensive.
Others in the field have realized the need to reduce the number of trips. An example of a mechanically set anchor with reduced trips is described in U.S. Pat. No. 3,908,759. A first trip mechanically sets a bridge plug having a latching member. In a second trip, the whipstock, attached to an end of a cutting mill, is engaged with the latching member, the connection to the mill is sheared, and the mill can begin cutting along the whipstock. The reference does not discuss how orientation is determined to properly set the whipstock in position in the two trips.
An example of a hydraulic anchor, a whipstock and a cutting tool assembly that is set in a single trip is described in U.S. Pat. No. 5,154,231. The anchor and whipstock are set under hydraulic pressure and held by mechanical interlocks. Rotation of the cutting tool shears the connection from the whipstock and the cutting tool can begin to cut the exit. However, the reference does not state how the angular orientation of the whipstock is achieved in the single trip.
Angular orientation of the whipstock in the wellbore is important to properly direct the drilling or cutting. Most methods of orientation and initiation of cutting require multiple trips. Some systems allow orienting and setting of the whipstock in a single trip of a drill string in combination with a wireline survey instrument. For example, a known system includes an anchor, a whipstock and a cutter connected to a drill string. A wireline survey instrument is inserted through the drill string to determine proper orientation prior to setting the whipstock. However, it is frequently necessary to circulate drilling fluid through the drill string at a low flow rate in order to push the wireline tool from the surface down to the region of the whipstock. The flow can prematurely set the anchor, unless some device such as a selectively actuated bypass valve is used to divert the flow. Further, such methods require the separate use of the wireline survey instrument.
In contrast to the use of wireline survey instruments, the oil field industry is increasingly using in-situ systems that are capable of collecting and transmitting data from a position near the cutting tool while the cutting tool is operating. Such position measuring tools are known as measuring-while-drilling (MWD) tools and are generally situated at the lower end of the drill string above the cutting tool. The MWD tools typically transmit signals up to surface transducers and associated equipment that interpret the signals.
However, using an MWD tool in an assembly with a hydraulic anchor has challenges. Typical MWD tools require drilling fluid flow rates even greater than the flow rate required to push the wireline survey instrument downhole and increases the likelihood of inadvertently setting the anchor. Thus, an increased flow rate bypass valve can be used as described in U.S. Pat. No. 5,443,129. However, the system is suitable for a typical drill string that is rotated by a conventional drilling apparatus on a surface derrick. The disclosure does not address the current trends of using more flexible coiled tubing requiring a downhole motor to rotate the cutting tool without substantially rotating the coiled tubing.
Coiled tubing is increasingly being used to lower the costs of drilling and producing a well. Coiled tubing is a continuous line of tubing typically wound on a reel on a mobile surface unit that can be inserted downhole without having to assemble and disassemble numerous threaded joints of a drill string. However, the coiled tubing is not sufficiently rigid to accommodate rotational torque from the surface of the well along the tubing length to rotate the cutting tool in contrast to systems using drill pipe. Thus, typically, a downhole motor is mounted on the coiled tubing to rotate a cutting tool. Drilling fluid flowed through the interior of the coiled tubing is used to actuate the motor to rotate the cutting tool or other members.
A typical motor attached to the coil tubing is a progressive cavity motor. FIG. 1 is a schematic cross sectional view of a power section 1 of such a progressive cavity motor. FIG. 1A is a schematic cross sectional view of the downhole motor shown in FIG. 1. Similar elements are similarly numbered and the figures will be described in conjunction with each other. The power section 1 includes an outer stator 2, an inner rotor 4 disposed within the stator. An elastomeric member 7 is formed between the stator and rotor and is typically a part of the stator. The rotor 4 includes a plurality of lobes 6 formed in a helical pattern around the circumference of the rotor. The stator includes a plurality of receiving surfaces 8 formed in the elastomeric member for the lobes 6. The number of receiving surfaces is typically one more than the number of lobes. The lobes 6 are produced with matching lobe profiles and a similar helical pitch compared to the receiving surfaces in the stator. Thus, the rotor can be matched to and inserted within the stator. Fluid flowing from the inlet 3 through the motor creates hydraulic pressure that causes the rotor 4 to rotate within the stator 2, as well as precess around the circumference of the receiving surfaces 8. Thus, a progressive cavity 9 is created that progresses from the inlet 3 to the outlet 5 as the rotor is rotated within the stator 2. Fluid contained within the cavity is thereby exhausted through the outlet 5. The hydraulic pressure, causing the rotor to rotate, provides output torque for various tools attached to the motor.
It is desirable to orient an anchor and a whipstock with a cutting tool, a downhole motor, an MWD tool and a downhole orienter coupled to coiled tubing, then set the anchor and whipstock and begin cutting an exit in a minimum number of trips. However, fluid flowed through coiled tubing to operate the MWD would also typically actuate the motor. Thus, the rotating motor would be changing the orientation of the downhole anchor and whipstock indicated by the MWD, making orientation difficult at best.
There remains a need for a system and method for orienting and setting an anchor and/or whipstock using coiled tubing with a cutting tool and a downhole motor coupled thereto.